Railway signaling apparatus



June 29, 1923. 1,459,999

K A. E. TATTERSALL RAILWAY S IGNALI NG APPARATUS Filed Feb. 24, 1921 d i FL OURRMT TRA Maro/PM 2 F'IG.

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atented lune 26, 13.

swear TATTERSALL, or naamw, Euer.

-RAJLWAY .SIGNALING APPARATUS.. v

applicati@ are@ February ai, 1921. serial un. einem. i

(GRANTED UNDER THE PROVISIONS 50E THE ACT OFMARCH 3, 1923., d1 STAT. L., 1313.)

To all whom it may concern.

Be it known that l, ARTHUR EWART TAT- frmzsaLL, a subject of the King of Great Britain and Ireland, residing at Harrow, England, whose post-oiice address is Radley,l Welldon Crescent, Harrow, in the county of Middlesex, England, have invented certain new and useful lmprovements in or Relating to Railway Signaling Apparatus; and l do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to railway signaling systems and apparatus, and in particular to track circuit signaling systems and apparatus of the kind in which an alternating electric current is fed to each track section and is adaptedto operate or control a track relay belonging to that section in such a exceed this amount.

manner that the relay is energized or not according to the absence from or presence on the section of track of a train, or pair of wheels and axle, the relay in turn controlling other signaling apparatus.

The present invention has for its principal object to provide a system or apparatus in which the shunting effect is considerably improved, compared with present systems, and rendered comparable to that obtained in direct current track circuit signaling. apparatas. l

The maximum safe shunt impedance of a track circuit may be defined as the maximum impedance which connected from rail to rail will divert sufficient current from the relay to cause-it to Vbe de-energized. Whatever this maximum' may be, it follows that for the safe operation'of the track circuit, when the track section is occupied by a train or vehicle, theimpedanc'e offered to the alternating track 'current from rail to rail through the wheels and -axles must not With present alternating current track.` circuit systems` the maximum safe shunt impedance is considerably less than the maximum safe shunt resistance of direct current track circuits (chiey due to the lower impedance of alternating current relays compared with direct current relays` andthe fact that alternating current relays require more poweial for their energization lthan direct currentI relays) and there is consequently a corre-y sponding increase in the current supplied to the track when occupied, such increase being of course objectionable as vit tends to keep the maximum shunt impedance at a low value.

rlhe present invention consists principally in providing, in a system of the kind above mentioned, means whereby the maximum shunt impedance of the track circuit is materially increased so that the system Will work efficiently under varying conditions met with in practice. Further according to this invention the maximum safe shunt impedance is increased by the employment of efficient means for maintaining a constant value of the current being delivered to the track circuit whether or not the track circuit is occupied by a vehicle or a pair of wheels and axle. Also according to this invention the maximum safe shunt impedance is still further increased by the employment of means for increasing the impedance of the relay circuit and thereby the total impedance of the track circuit. The shunting effect is so improved, bythe present invention, as to insure that, under various Working conditions met with in practice, the track rela shall be de-energized by the entrance o a train or a pair of wheels and axle on the rails ot' the track circuit. Further the apparatus according to this inven-` tion is simple, and is less liable to get out ot' proper working order than is the case with previously proposed systems.

ln systems heretofore proposed and employed the track circuit is fed withalternating current from the secondary of a potential or pressure transformer the primary of which receives its current from a power line or other suitable source ot' alternating current, and the supply ot' current to the trackcircuit isregulated bv means of a resistance or impedance inserted in series with the secondary of the transformer and the rail cir'- cuit, a suitable alternating current track relay being connected to the rails of the circuit in the usual or any suitable manner.

According to the present invention, the trac-k circuit is fed with alternating current from the secondary of a constant current transformer arranged in circuit with the rails of the insulated track section, the primary of this transformer receiving its current from a power line or other suitable source of alternating constant current. This current transformer may be of any approved iype which utilizes` the feature of phase isplacement to insure the delivery of a constant current to the track whether the track be occupied by a train or not. ln one type the magnetic leakage path between the primary and secondary windings is considerable, any tendency for an increase of current due to a decrease in the impedance ot' the secondary circuit i. e. the transformer` secondary, in the track circuit being counterbalanced by a drop of pressure from seliinduction.` The current output or supply to the track circuit will therefore remain constant. ln another well known type, the secondaries consist of two Hoating coils counterbalanced against the electro-magnetic repulsion oi the primary coils and also balanced against each other. The primaries are fixedy at the to and bottom of the Vertical -double leg dp core and work at a. constant potential. Any change in the relative positions of the coils alters the re-actance of the combination and the balancing of the movable secondaries is so arranged that any change in the current value will immediately rauserthe coils to assume a new position and restore the current to its former value by the change in re-actance thus produced.

rlhe constant current transformer renders the provision of the ordinary regulating resistance or impedance between the transformer secondary and the rails unnecessary, thus effecting economy in power consump tion in the track-circuit represented by the track rails and track relay, this being a iurther advantage ot the present invention.

Further according to this invention a suit able condenser or a suitable impedance is provided in the connection ofthe primary of the aforesaid current transformer to the source ot supply of alternating current, either alone or in combination, the condenser alone being ythe preferred arrangement. Thecondenser or the impedance (or both if employed in combination) may be provided with adjustable steps so that the capacity and re-actance, or capacity, re-actance and impedance may be varied in order that the current being delivered to the track circuit may be varied 'to suit the insulation value ot the track circuit. lt is also found that this arrangement assists in maintaining a goed regulation. of the transformer, but its prihereinbeiore mentioned method et improv.

.ma-ry urpose is to afford an economical method of varying the current supplied to the track circuit according to the impedance of the track circuit.

By the means thus far described a prede- `termined current value in the track circuit can be kept practically constant, whereby the shunt effect is considerably7 improved.

Further according to this invention, for further improving the shunting eect by increasing the impedance of the relay circuit as hereinbefore mentioned a relay of higher impedance than those at present used may be employed, or a suitable resistance or im-4 pedance may be inserted in series with the relay. and vin yet a further embodiment of matic view illustrating an. insulated section of railway Vwith alternating current track circuit supplied with current `from a suitable source 1 of alternating current, and shows the hereinbei'ore mentioned const-ant current transformer 2 with its primary coil 3 connected'to the leads of the supply l and with its secondary coil i connected to the rails of the insulated track section. This figure also shows the hereinbefore mentioned condenser and the hereinbet'ore mentioned suitable resistance or impedance tl connected in series with the supply l and the primary 3 ot the transformer. vi' is the` usual or any suitable track relay connected as usual tothe rails of the track circuit section, 8 being the usual tongue or armature of this relay controlling. through the contacts 9, the local circuit of the signal l0 as usuahl f ln the diagrammatic view Fign 2, il is the hereinbefore mentioned resistance or impedance inserted in series, with the rails ot the track circuit and the relay 7,

The diagrammatic view Fig. 3, shows the bereinbefore mentionedV condenser i2., and impedance 13, connected in series with the source of alternating current supply l and the local coil la or a double element relay l5 of known or suitable type. This figure illustrates the system adapted for use on electrically operated railways employing an earthed traction return, i6 indicating the usual re-actance bonds employed in such a case. 0n electrically operated railways em.-

ploying an insulated traction return, erin locations Where the relay requires te beprotected against extraneous currents, a reiay isolating transformer is em loyed.

Referring to Fig. 2 whic iilustrates the ing the shunt effect by increasing the imf pendance oit' the relay circuit, it may be mein tioned that this method has been atterupted;`

with existing systems but owing to the emi' ployment of a regulating resistance or im.- pedance in series with the secondary of a potential or pressure transformer, the value of the extra impendance in the relay circuit had of necessity to be-very small in order to keep the circuit as economical as possible, (as it is evident that the secondary pressure of the track transformer has to be increased to suit), so that the improvement in the shunting effect is not as great as in the present invention. In the present invention, however, owing to the employment of a current transformer in combination with either the condenser 5 or impedance 6, or both,

-" and to thc ordinary regulating resistance or impedance not being employed, the value of the inserted resistance (ll-F ig 2) in the relay circuit can be made such that, for the same track power consumption as in existing systems, the shunting effect is greatly improved.

Where two-element track relays are employed, it is necessary to employY some agency whereby the currents in the two relay windings are either brought in phase, or 90 out of phase, according to the type of relay employed With 'existing systems, this 4is usually accomplished by arranging the power factor ofthe regulating resistance or impedance to suit, or by providing what is known as a 'shielding winding at the relay. In many cases, especially with the polyphaSe induction relay, neither of these methods is entirely satisfactory, with the result that the track current has to be increased in order tto provide the necessary torque at the relay, tnd this decreases the shunting effect. In the present invention the necessary phase relationship is provided, by the means above described with reference to Fig. 3, in a certain and economical manner as compared with previous systems.

By thus providing the phase relationship between the local and the track circuit windings (respectively 14, 15) of the relay, less current is required in the track circuit to satisfactorily operate the relay and the shunting effect is consequently improved. Further the action of the relay itself is improved owing to absence of chattering at the relay contacts.

What I claim as my invention and desire to secure by Letters Patent is l. The combination, with a track section havino insulated rails, of a constant current transtbrmer having primary and secondary coils, leads connectlng the primary coil with a source of alternating current, leads connecting the `-secondary coil with the said rails, the said transformer hav-ing a large magnetic leakage and operating to maintain a constant current in the secondary circuit whether the rails are occupied by a train or not, and a local ,circuit operatively connected with the said rails and having a signal and a relay included in it.

2. The combination, with the -device set i forth in claim l, of means included in series in the primary circuit which operate to regulate the current in the primary circuit so as to vary the current in the secondary circuit` to suit the insulation value of the rails. In testimony whereof I allix my signature. in presence of two witnesses.

ARTHUR EWART TATTERSALL. Witnesses:

W. Hnz SIMMs, W. F. LINSON. 

